Making process control valve choices Professionalمنذ أسبوعين - Multimedia - Saïda - 18 الآراء
One of the main areas of debate when specifying control valves is determining the size of the valve required. Often process engineers will know the pipe diameter used in an application and it is tempting to take that as the control valve’s defining characteristic. Of greater importance are the flow conditions within the system as these will dictate the size of the orifice within the control valve. The pressure either side of the valve and the expected flow rate are essential pieces of information when deciding on the valve design.
Inside the valve body, the actuator design is often either a piston or a diaphragm design. The piston design typically offers a smaller, more compact valve which is also lighter and easier to handle than the diaphragm designs. Actuators are usually made from stainless steel or polyphenolsulpide (PPS), which is a chemically-resistant plastic. The actuator is topped off by the control head or positioner.
Older, pneumatically operated positioners had a flapper/nozzle arrangement and operated on 3-15psi, so no matter what the state of the valve, open closed or somewhere in between, the system was always expelling some compressed air to the atmosphere.
Compressed air is an expensive commodity, requiring considerable energy to generate and when a manufacturing line is equipped with multiple pressure relief valve all venting to the atmosphere, this can equate to a considerable waste of energy. It is important to not only establish the most appropriate valve design, but also a cost-effective solution that takes account of annual running costs.